3V3 in, 5V out buffer driver

roll your own !

Marc

I would but my silicon foundry is down ;-)

What I meant is I would expect to find ready made discrete buffers for doing this task. In my case I want to get a 5V SPI interface from a 3V3 uP. An oc solution is problematic because the line has to run around several devices at several MHz......I need a good pp output, but that requires 2 buffers, an oc to shift and a line driver.

Take a look at TI's site:

Near the bottom of the page is a section called "Voltage Level Translation". The parts are similar to a 16-bit version of a '245, however the dual voltage versions have for example a 3.3V Vcc on left side of the chip, and a 5v VCC on the right side of the chip. The SN74ALVC164245 chip, for example has 48 pins with a 0.35mm (0,025") lead pitch. There are many GND and power pins, which reduce ground bounce and other nasty things when all 16 signals switch at once. There are also Bus Switches, which are just FETs that connect side-A to side-B. Simple logic controls whether the switches are on or not. These should work OK for 5-TTL to 3.3V CMOS, but AFAIK won't work correctly with 5V CMOS.

TI has a variety of voltage translation chips as do other manufacturers, who I can't remember right now ;( . HTH

-Dave Pollum

This looks like what I was looking for:

SN74LVCC3245A

A '245 with seperate supplies for each side :-)

Judging by the stock levels at Dkey these things are used in vast quantities. I must be blind ;-)

74HCTxxx, if they are fast enough for your application.

--
WBR, Yuriy.
"Resistance is futile"

I might suggest the SN74LVC4245A, bi directional 3.3V5V transcievers. They cost all of about $0.50 from digikey.

Why do you persist in a bad solution when the STATIC overlap current has been shown to be quite large in previous threads?

The "LVC" parts are the proper way to go.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

For cheap solution, from 3.3V logic to 5V logic can use the 74HCTxxx series. These IC use 5V power with near 5V Voh and allow 2.0V as Vih. For 5V logic to 3.3V logic can use the 74LVC series. These IC have 5V tolerance in inputs. For bi-direction ports, only 74LVC4245 series dual power devices can be used.

"Roger" ???????: snipped-for-privacy@n67g2000cwd.googlegroups.com...

RTFM.

You really need to educate yourself; "Art of Electronics" will be a good primer. After that read the #$%@ datasheet. LVC family: Vcc = 3.5V for single supply LVC parts if Vcc=5.0V is allowed. dIcc up to 0.5mA for dual power LVC parts @ Vcc=3.3, Vin=2.7V

--
WBR, Yuriy.
"Resistance is futile"

Your ignorance is profound. Go back and read all the way through the original thread on this topic. There you will find that another poster likewise criticized my opinion, THEN went and MEASURED a

74HCTxxx part at 3.3V input with VDD=5V, and measured the ENORMOUS overlap I warned about.

You are herewith relegated to s.e.b until you grow up.

PLONK!

BTW, Don't you even dare to tell me what I should read. I could write the whole f****ng book without once looking up a single reference.

And do loop and nodal analysis ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

How much does it get? I would expect low enough so the parts will be in spec over temperature, but can you give some figure? I am sure I have used this configuration and I never had any trouble out of it, but I have not been looking for the last milliwats. Never noticed a part getting hot because of that, though.

Dimiter

------------------------------------------------------ Dimiter Popoff Transgalactic Instruments

------------------------------------------------------

Jim Thomps>

[snip]

Agent dumps old threads after 10 days so I can't go back and look, but I believe it was on the order of 4-5mA, which I consider unacceptable for static consumption.

Maybe the OP will return with his data ??

My main point is: WHY do it when good-engineering-practice solutions exist?

Of course, if you're a hacker, who cares ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I wish Jim would give us a link or thread title, I can't find the post he's referring to. TI's 74hct14 datasheet has a plot of the supply current, and it's only 0.1mA with a 3.3-volt logic input, for the extreme case of a 5.5-volt supply. If you assume a wimpy 2.8-volts (degraded 3.3V input) it's 0.15mA, not what most people call an ENORMOUS current. (That is, unless you designed for the long-life battery-operated field, as I did for 17 years, where our entire budget to operate 200 ICs was often about 150uA.)

TI specs the maximum current for a HCT14 single 2.4-volt input as 2.9mA and the maximum for a VHCT14 is 1.5mA with 3.4V input. The real-world currents for both families will be much lower. Neither is a deal-breaker for most circuits, since even 15mW dissipation would usually not be a problem. It can't lead to overheating!

BTW, Jim's suggested AVC logic series can't work to convert 3.3 volt logic to nice 5 volt swings, as Yuriy complained, because the AVC stuff can't be operated on a 5-volt supply. The 3.3V output of a AVC logic gate would simply pass the problem on to the next HCTxxxx 5V logic gate.

Interesting company name!

--
 Thanks,
    - Win

4-5 mA per input is indeed a lot, I guess I'll switch over next time I have a chance. I remebered now an aplication in which I used HCT367s - 3 of them - driven by the 3.3V outputs of a DSP, statically, to switch a 3x3 latching relay matrix; at least 6 inputs on all 3 chips are constantly at 3.3V (just driven low for a few milliseconds when a relay is to be turned over). This could amount to, let me see, 5*6*5=150 mW! The entire device consumes appr. 2W and this would have been the last place I would look at to save a milliwatt or two, I thought I had a 0 there... :-).

Dimiter

------------------------------------------------------ Dimiter Popoff Transgalactic Instruments

------------------------------------------------------

Jim Thomps>

Well the HCT14 is perhaps not typical when it comes to its inputs, being Schmitt-triggered; I expect special precautions have been taken with it (and the 132 etc.). I'll take some measurements next time I have a chance to do so, I really would not have expected to spend milliwatts of, well, hard to neglect significance, on _that_.

Thanks! To quote from my "who we are" file:

" The name originates from the dark communistic ages (around 1980) when dreaming of a private high-tech company was regarded more like a health issue so there had to be some sense of humour in it besides the hard work (done in an attick back then). "

:-) :-)

Dimiter

------------------------------------------------------ Dimiter Popoff Transgalactic Instruments

------------------------------------------------------

W> >

I doubt it was that high. If so, we need to know what manufacturer, because it's far above the clearly-stated maximum specs.

Why cast aspersions against standard industry practice, especially when your suggested LVC alternate simply can't work? What are you suggesting instead?

I note that ON Semi's mc74vhc1gt32 (were you involved with that product?) specifically states "to be used as a logic?level translator from 3.0 V CMOS logic to 5.0 V CMOS Logic", yet it has exactly the same "problem" and draws 1.5mA max for 3.4-volt inputs with 5V supply, just like the standard hct and vhct logic families.

--
 Thanks,
    - Win

Really ?:-)

I showed a schematic awhile back that had no such current. The *true* logic translators usually have two VDD's... one at 3.3V and one at 5V.

I don't recognize "VHC"... the stuff I did was "LCX"; and there's a project file that I know of only as "TinyCkts"... I don't know what naming convention those ended up under.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I didn't suggest any such thing. Someone mentioned a part number, which I can't recall now, that did proper translation... at the time I checked the data sheet, but can't recall the prefix now.

Win, Are you saying that 74HCTxxx is a good-engineering-practice solution for 3.3V-to-5V translation?

Maybe at Harvard ?:-) But at MIT they periodically show the Galloping Gerty movie to remind everyone that half-assed design always ends up a failure ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I'm sorry, I meant to say LVC (correct in my 2nd post). This per your 18 Dec message, "The "LVC" parts are the proper way to go."

Most of the LVC parts cannot be powered from 5 volts. A few, like TI's 74lvc1g32 can, but that one shouldn't be used with 3.3V logic. If there's an ideal LVC part, by your terms, I haven't found it.

One perfectly good practice, yes. If it's specified on the data sheet, as it is for most if not all HCT families, such as the TI parts I mentioned. One should check the part in question. As I said, many of ON Semi's parts have the same specs, including some of the proprietary ones, like the mc74vhc1gt32, specifically labeled a logic-level shifter. They all use the same approach you are ridiculing. What's your problem with < 15mW?

BTW, this has nothing to do with Harvard or MIT (you should see some of the electronics stuff I see over at the Media Lab).

--
 Thanks,
    - Win